public class CircularList {

    private ListItem marker;

    CircularList() {
        marker = null;
    }

    public void insert(Object x) {
        if (isEmpty()) {
            //  why can't the following two lines be done at the same time?
            marker = new ListItem(x,null);
            marker.setNext(marker);
        }
        else
            marker.setNext(new ListItem(x, marker.getNext()));
    }

    public Object delete() {
        if (isEmpty())
            return null;
        else {
            Object temp = marker.getNext().getItem();
            if (marker.getNext() == marker)
                marker = null;
            else
                marker.setNext(marker.getNext().getNext());
            return temp;
        }
    }
    public Object head() {
        if (isEmpty())
            return null;
        else
            return marker.getNext().getItem();
    }
    public void move() {
        if (marker != null)
            marker = marker.getNext();
    }
    public boolean isEmpty() {
        return (marker == null);
    }
    public String toString() {
        String result;
        if (isEmpty())
            result = "empty list";
        else {
            ListItem head = marker.getNext();
            marker.setNext(null);  // break the cycle
            result = head.toString();
            marker.setNext(head);  // put the cycle back
        }
        return result;
    }
}